LABORATORY STUDIES ON THE ANAEROBIC SEQUENCING BATCH REACTOR

The anaerobic sequencing batch reactor (ASBR) is a new high rate anaerobic process (U.S. Pat. No. 5,185,079) that has been under development by Dague and co-workers at Iowa State University. In the research reported in this paper, four, 12-L ASBRs of different configurations were operated at a constant temperature of 35 degrees C. The objectives of the work were to evaluate the fundamental factors affecting solids separation in the ASBR, including reactor configuration, mixing (continuous versus intermittent), gas-production rate, mixed liquor suspended solids concentration, and bioflocculation-granulation, and to determine the effect of these factors on the performance of the ASBR treating a soluble, synthetic substrate (nonfat dry milk). The ASBRs were capable of achieving in excess of 90% soluble chemical oxygen demand (COD) reduction on the synthetic milk substrate over a range of COD loadings from 2 to 12 g/L . d at hydraulic retention times of 48, 24, and 12 hours. Reactor configuration is significant in the development of granular sludge. Relatively tall, slender reactors tended to select for granules better than the short, stout reactors. However, the shorter reactors were capable of accumulating higher concentrations of biomass than were the tall reactors. intermittent mixing was found to be preferable to continuous mixing from both COD removal and methane production standpoints.